[ExI] Expansion of the Universe

[BillK]

On Sun, Dec 30, 2012 at 12:16 AM, Anders Sandberg  wrote:
> You are essentially arguing that the large-scale metric is dominated by the
> Weyl part of the the metric tensor (gravitational waves) and that the
> universe is not isotropic. I think some people have looked at it, since the
> standard models are isotropic, but there is *no* evidence for very large
> scale anisotropy. The closest things are hints that there might exist some
> weird twists and axiality to large-scale spacetime, but I have not seen any
> follow-up from the original claims.
>
> What you suggest is very very large scale isotropy, so that the wavelengths
> are large enough not to be visible to us right now. I don't have enough
> "feel" for the Friedman equations to tell how this would play out. But I
> suspect the isotropic and homogeneous expansion would swamp the waves: they
> become more dominant in collapsing Mixmaster universes, so I suspect the
> opposite would be true for an expanding universe.
>
>

See: <http://map.gsfc.nasa.gov/>

Wilkinson Microwave Anisotropy Probe

The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA Explorer
mission that launched June 2001 to make fundamental measurements of
cosmology -- the study of the properties of our universe as a whole.
WMAP has been stunningly successful, producing our new Standard Model
of Cosmology.

The WMAP science team has…

    ... has put the "precision" in "precision cosmology" by reducing
the allowed volume of cosmological parameters by a factor in excess of
68,000. The three most highly cited physics and astronomy papers
published in the new millennium are WMAP scientific papers---
reflecting WMAP's enormous impact.

    …mapped the pattern of tiny fluctuations in the Cosmic Microwave
Background (CMB) radiation (the oldest light in the universe) and
produced the first fine-resolution (0.2 degree) full-sky map of the
microwave sky.

    …determined the universe to be 13.77 billion years old to within a
half percent.

    …nailed down the curvature of space to within 0.4% of "flat" Euclidean.

    …determined that ordinary atoms (also called baryons) make up only
4.6% of the universe.

    …completed a census of the universe and finds that dark matter
(matter not made up of atoms) is 24.0%

    …determined that dark energy, in the form of a cosmological
constant, makes up 71.4% of the universe, causing the expansion rate
of the universe to speed up. - "Lingering doubts about the existence
of dark energy and the composition of the universe dissolved when the
WMAP satellite took the most detailed picture ever of the cosmic
microwave background (CMB)." - Science Magazine 2003, "Breakthrough of
the Year" article

    … mapped the polarization of the microwave radiation over the full
sky and discovered that the universe was reionized earlier than
previously believed. - "WMAP scores on large-scale structure. By
measuring the polarization in the CMB it is possible to look at the
amplitude of the fluctuations of density in the universe that produced
the first galaxies. That is a real breakthrough in our understanding
of the origin of structure." - ScienceWatch: "What's Hot in Physics",
Simon Mitton, Mar./Apr. 2008.

    …detected that the amplitude of the variations in the density of
the universe on big scales is slightly larger than smaller scales.
This, along with other results, supports "inflation", the idea is that
the universe underwent a dramatic period of expansion, growing by more
than a trillion trillion fold in less than a trillionth of a
trillionth of a second. Tiny fluctuations were generated during this
expansion that eventually grew to form galaxies.

    … determined that the distribution of these fluctuations follows a
bell curve with the same properties across the sky, and that there are
equal numbers of hot and cold spots in the map. The simplest version
of the inflation idea predicted these properties and remarkably,
WMAP’s precision measurement of the properties of the fluctuations has
confirmed these predictions, in detail.
---------------


Amazing science work!


BillK